EP0885662A1 - A method and an apparatus for adhering particles to an object by supplying air ions - Google Patents

Abstract

The present invention relates to a method and anapparatus for adhering particles on an object to form acoating thereon. The particles are sprayed onto the objectin which the air ions comprising positive air ions andnegative air ions are continuously supplied to both sprayedparticles in an atmosphere and a surface of the object to becoated during a spraying operation. The apparatus comprisesa chamber for accommodating the object and an air ionizerwhich is provided at a ceiling or a side wall of the chamber,and the ionizer receives an air from the outside of the chamberand produce the positive and negative air ions to supply inthe chamber.

Description

FIELD OF THE INVENTION

This invention relates to a method and an apparatus foradhering particles to an object to form a coating thereon andmore particularly to a method and an apparatus for sprayingpaint particles to the object. In the specification, anexplanation of the invention is directed to a painting butthe idea of the invention is applicable to other techniquewhich includes a printing, an adhesion for example.

BACKGROUND OF THE INVENTION

For a painting, a good finishing of coating and a goodefficiency of adhesion of paint particles are required. Anelectrostatic painting is widely used to acquire the latterrequirement in which a paint spray gun is to be charged bya first potential and the spray gun emits charged paintparticles, a target to be painted is to be charged by a secondpotential so that the electrically charged paint particlesemitted by the spray gun have a first electric force appliedto them urging the electrically charged paint particlestoward the target. According to the electrostatic painting,the efficiency of adhesion of particles is increased and anamount of waste particles is greatly reduced.

It is, however, that according to the electrostaticpainting, a force of collision between the particles and thetarget is strong so that a forming of an adhesion layer isrough which results in a bad finishing of a surface. Inaddition, safety measures add substantially to the cost,complexity and bulk of the electrostatic paining apparatus.

The present invention is mainly directed to provide anew method and an apparatus for adhering particles to theobject in which, by supplying air ions, the good finishing of coating is obtained and the efficiency of adhesion isimproved.

Generally, the air ions are used to neutralize the staticcharges. It is well known that a high concentration of bothtypes of air ions acts to suppress accumulations of staticelectricity on objects to be coated. Static electricalcharges attract air ions of the opposite polarity and theattracted ions then neutralize the static charges. In apre-painting process, a use of ionizer which produce bothpositive and negative ions is known. For example, a spraybooth in which the air ions are introduced into a chamber toneutralize and suppress a static electric charge and preventa dust from clinging to an object to be coated is disclosedin Japanese laid-open patent No. 8-84948 and Japanese UtilityModel Registration No. 3018050.

SUMMARY OF THE INVENTION

According to the present invention, in a method foradhering particles on an object to form a coating thereon,particles are sprayed to the object in which air ionscomprising positive air ions and negative air ions arecontinuously supplied to both sprayed particles in anatmosphere and the surface to be painted. The present methodis different from the prior arts in above-mentioned Japanesedocuments in that the air ions are continuously suppliedduring a spraying operation. According to the present method,the coating of good finishing and the good adhesion betweenparticles themselves and between the particles and thesurface to be coated are obtained.

It is believed that the air ions comprising the positiveand the negative air ions affect the paint particles and thesurface to be painted somehow thereby contributing to the goodadhesion between the particles and the surface to be coatedand the good adhesion between particles themselves. Thewetting property of the surface may be improved by continuously supplying the air ions to the surface. Thesprayed particles in the atmosphere may be charged bycontinuously supplying air ions to the sprayed particles andthe charged particles are electrostatically attracted eachother resulting in the good adhesion between the particles.The surface(which includes a surface of layer of paintedparticles as well as the surface of the object) may be chargedby continuously supplying the air ions to the surface.Considering the fact that a thickness of the coating of paintparticles of the present invention is thicker than that ofnormal spraying, other spraying conditions being equal, anelectrostatic force may be something to do with the formationof coating.

Though the mechanism of formation of coating is notclearly understood, according to a hypothesis, the particleis charged in which the particle has both a positiveelectrostatic charge and a negative electrostatic charge atopposite positions each other. The particle which normallyhas a positive electric charge at first when it is sprayedmay be neutralized by the negative ion, but by continuouslysupplying positive and negative ions to the particle, theparticle may be charged according to Fig. 1 (a) and portionsof opposite electric charges attract each other to form alayer as shown in Fig. 1(b). According to this hypothesis,it is desirable to supply equal numbers of positive andnegative ions to the particles and the surface to be painted.

The object to be coated is made of any materials suchas metal, wood, plastic, paper and the like. The particlesare made of water-soluble paint particle, powder paintparticle, organic-soluble paint particle, ink and the like.It is found that the organic-soluble paint particle and thepowder paint particle are preferably selected. It is foundthat in case of the water-soluble paint particles,preferably, the positive ions and the negative ions are alternately supplied to the particles at predeterminedinterval, a few seconds for example. Preferably, an air-lessspray such as a centrifugal spray is selected. In case of anair spray, the air ions may be diluted by a sprayed air.

According to the present invention, a spray boothapparatus for spraying particles to an object by continuouslysupplying air ions of positive air ions and negative air ions,the apparatus comprises a chamber for accommodating theobject and an air ioniser which is provided in a ceiling ora side wall of the chamber to supply both the positive airions and the negative air ions in the chamber.

Preferably, the ionizer comprises at least a pair of airionizing electrodes and a D.C. voltage supply which producesboth positive and negative high voltages to apply voltagesof opposite polarities to the ionizing electrodes. Accordingto a D.C. voltage type ionizer, it is easier to control a ratioof the production of the positive ions and the negative ions.

More preferably, the ionizer further comprises means forinterchanging the polarities of said ionizing electrodes ata predetermined interval. An erosion of the positiveelectrode progresses faster than that of the negativeelectrode because molecules are collided with the positiveelectrode at the time of corona discharging. Because of theinterchange of the polarities of the electrodes, theelectrode erosion of both electrodes are averaged therebypreventing an imbalance of production of positive andnegative ions and prolonging the life of the electrodes. Inaddition, the interchange of the polarities of the electrodesprevents the dust from clinging to the electrodes.

In another aspect of the invention, the ionizercomprises at least one air ionizing electrode, a D.C. voltagesupply which produces both positive and negative highvoltages to apply a voltage of either of polarity to theionizing electrode and means for interchanging the polarity of the ionizing electrode at a predetermined interval. Thistype of ionizer is preferably used for the water-solubleparticles.

According to the method of the present invention, thecoating having a strength is obtained because of the goodadhesion between the particles. Accordingly, by sprayingparticles on the surface of liquid such as water, the coatingin formed on the surface. The coating may be removed from thesurface and obtained as a film. Alternatively, by pressingan object onto the coating, the coating is transferred to thesurface of the object by a liquid pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1 shows a model of charged particles in an atmospherecomprising positive air ions and negative air ions.

Fig.2 is a schematic view showing a method of the presentinvention.

Fig.3 (a), (b) are side elevations showing two types ofspray booths.

Fig.4 is a perspective view of a charging unit of an airionizer of the present invention.

Fig.5 is a perspective view showing a control unit ofan air ionizer of the present invention.

Fig.6 shows interchanges of polarities of electrodes.

Fig.7 shows a high voltage supply.

Fig.8 is a circuit diagram showing a first embodimentof the interchanges of polarities.

Fig.9 is a circuit diagram showing a second embodimentof the interchanges of polarities.

Fig.10 shows another embodiment of a method for coating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig.2 shows a painting method of the present invention.An air introduced is cleaned by an air filter and is inonizedby an air inonizer and positive air ions and negative air ionsare produced. The positive air ions and the negative air ions are supplied to a surface of an object to be painted. Thenpaint particles are sprayed to the surface of the object.During a spraying operation, the air ions comprising thepositive air ions and the negative air ions are continuouslysupplied to both sprayed particles in the atmosphere and thesurface to be coated.

As shown in Fig. 3, a spray booth comprises achamber 1for accommodating the object to be coated, anair inlet 2 andanair outlet 3, and theair ionizer 4 which is provided ina ceiling of thechamber 1 and is adapted to receive the airfrom the outside of thechamber 1 to generate both positiveand negative ions and supply them into thechamber 1.Preferably, the air introduced is cleaned by an air filter.In thechamber 1, the object is placed to receive an ionshower. In case of a spray booth, by continuously supplyingthe air ions, thechamber 1 is filled with air ions and anatmosphere comprising positive ions and negative ions isobtained. When the paint particles are sprayed in thatatmosphere, the air ions are supplied to the sprayedparticles.

Theair ionizer 4 comprises acharging unit 5 which isprovided in an upper wall and/or a side wall of thechamber1 and apower control unit 6 which is separated from thechargingunit 5 and is provided outside thechamber 1.

The chargingunit 5 comprises four dischargingwires 7which constitute ionizing electrodes andcartridges 8accommodating the electrodes, first supportingmembers 9which extend along with thecartridges 8, second and thirdsupportingmembers 10, 11 which extend substantiallyperpendicularly to the first supportingmembers 9 and a D.C.voltage supply which produces both positive and negative highvoltages to apply voltages of opposite polarities to theionizing electrodes. The electrodes are spaced apart and areparalleled each other. Upper portions of thecartridges 8 are supported by the first supportingmembers 9. One ends ofthe first supportingmembers 9 are supported by the secondsupportingmember 10 and the other ends of the firstsupportingmembers 9 are supported by the third supportingmember 11.

The first and the second supportingmembers 9, 10 havea hollow portion therein and one ends of the first supportingmembers 9 are open ends and communicate with the secondsupportingmember 10. The second supportingmember 10 has acloned end and an open end and the open end is provided withanair hose 12 which supply an air from the outside of thechamber 1. The elongate cartridge a which accommodates theelectrode has aslit 8a which is provided at lower portionof thecartridge 8 and is extended in an extending directionof thewire 7. Theelectrode wire 7 is made of tungsten havinga diameter of 60 micron and has an Au plating.

The first supportingmembers 9 are slidably mounted atthe second and the third supportingmembers 10, 11 inextending directions of the second and the third supportingmembers 10, 11. Therefore, spaces between the electrodes canbe selected in accordance with the object to be coated.

Thepower control unit 6 comprises ablower 13, afilter14, acontrol panel 15 and an air inlet. The air flow createdby theblower 13 is supplied to thecharging unit 5 via theair hose 12. A rotation ofblower 13 and a charging of theelectrode are synchronized so that the entry of paintparticles to thecartridge 8 is prevented. An amount of airflow is also adjustable by controlling the rotation of theblower 13.

Theionizer 4 of the embodiment is a D.C. voltage typeionizer in which theelectrode wire 7 becomes a positiveelectrode by charging a positive D.C. voltage bias and theelectrode wire 7 becomes a negative electrode by charging anegative D.C. voltage bias. If two of the fourwires 7 are charged by the positive voltage and the rest twowires 7 arecharged by the negative voltage, theionizer 4 produces boththe positive ions and the negative ions at the same time.

The high voltage supply comprises a pair of transformersand the primary windings of transformers receive directcurrents and alternating currents are obtained at thesecondary windings of the transformers. The secondarywindings are connected to electrodes via multiplying andrectifyingcircuits 16a, 16b which comprise a plurality ofcapacitors 17 anddiodes 18 so that a high D.C. voltage ofeither polarity is applied to the electrodes.

According to theair ionizer 4 of the present invention,theionizer 4 comprises means for interchanging the polarityof the electrodes at a predetermined interval. A relay forswitching the polarity of D.C. current voltage which is tobe applied to the electrodes is comprised of amake contact19a and abreak contact 19b. When themake contact 19a isopend, thebreak contact 19b is closed and vice versa. Whenthemake contact 19a is closed, a switch 20a is switched onand acontact 21a for RL2 is closed so that the negative highD.C. voltage is applied to the electrodes. When thebreakcontact 19b is closed, aswitch 20b is switched on and acontact 21b for RL1 is closed so that the positive high D.C.voltage is applied to the electrodes. In this regard, Fig.8shows four electrodes and two a pair of high voltage suppliesin which two electrodes are connected to a first high voltagesupply of a first polarity and the rest two electrodes areconnected to a second high voltage supply of a secondpolarity. Fig.9 shows four electrodes which are connected toa high voltage supply in which high D.C. voltage of eitherpolarity is applied to all electrodes at the same time. Fig.6shows interchanges of polarity of electrodes in which (a)corresponds to the circuit of Fig.9 and (b) corresponds tothe circuit of Fig.8

Fig.10 shows another embodiment of a method for coating.In this embodiment, particles are sprayed on a surface of aliquid 22 such as water and acoating 23 in formed the surfacewhich is regarded as a first object. Thecoating 23 may beremoved from the surface and obtained as a film.Alternatively, a second object 24 is pressed onto thecoating23 and thecoating 23 in transferred to the surface of thesecond object 24 by a liquid pressure. The liquid 22 ispreferably selected according to the specific gravity of thecoating particles and in most cases, the water is preferablyselected. Thecoating 23 may be comprised of layers in whicha first layer of the surface is a clear coating, a second layeron the first layer is an enamel coating and a third layer onthe top is a primer coating.

example 1

	sample 1	sample 2
gloss	85.3 degrees	93.2 degrees
hardness	HB	2H
adhesion particulars	100/100	100/100
(1)substrate: ABS resin (sample 1 and sample 2) (2)spray condition: sample 1: an air atmosphere, 25 degrees Celsius, 55%humidity /enamel paint - 10 minutes´ setting - clear paint-drying(60 minutes, 70 degrees Celsius) sample 2: an air atmosphere, 25 degrees Celsius, 55%humidity + continuously supplying both positive air ions andnegative air ions during spraying operation/enamel paint -10 minutes' setting - clear paint- drying (60 minutes, 70degrees Celsius) (3)gloss: 60 degrees mirror surface reflection rate/ thedigital deflection angle gloss measuring instrument(UGV-50type Suga) (4)hardness: the pencil scratching instrument usingMitsubishi uni (Toyo Seiki) (5)adhesion:gobanme test after 240 hours in the water 40degrees Celsius/ the cross cut guide (Kotex)

Those examinations correspond to JIS(JapaneseIndustrial Standard) K 5400. As shown in the table 1,sample2 has advantages in gloss and hardness. Though the result ofadhesion is the same according to this test, it does not meanthat the strength of adhesion ofsample 1 andsample 2 areequal.

Example 2

	sample 1	sample 2
thickness particulars	40 micron	70 micron
(1)substrate: ABS resin of 20cm X 30 cm (2)coating: enamel paint (30g), clear paint (30g) (3)spraying condition sample 1: enamel paint - 10 minutes´ setting - clearpaint- drying ( 60 minutes, 60 degrees Celsius)-setting time2 hours sample 2: continuously supplying both positive airions and negative air ions during spraying operation/enamelpaint - 10 minutes' setting - clear paint- drying ( 60 minutes,60 degrees Celsius)-setting time 2 hours

The result of the example 2 shows that the present methodhas an advantage in forming a thicker coating.

According to the example 1 and 2, substantially equalnumbers of positive and negative air ions ire supplied.However, the ratio of the positive and the negative air ionsis not limited to the example. Some imbalances of the positiveand the negative ions are tolerable to obtain a preferableresult compared with the normal spray coating.

Claims (19)

1. A method for adhering particles on an object to form acoating thereon, said method comprising:

   spraying the particles onto the object; and

   continuously supplying air ions comprising positive airions and negative air ions to both sprayed particles inan atmosphere and a surface of the object to be coatedduring a spraying operation.
2. The method as claimed in claim 1, said method comprising:

   accommodating the substrate in a chamber;

   continuously supplying the air ions comprising thepositive air ions and the negative air ions in said chamberand obtaining an atmosphere comprising the positive airions and the negative air ions in said chamber; and

   spraying the particles to the object in said atmosphere.
3. The method as claimed in claim 1, wherein said particlesare water-soluble and the positive air ions and thenegative air ions are alternately supplied to the sprayedparticles and the object at a predetermined interval.
4. The method as claimed in claim 1, wherein the air ions aresupplied by an air ionizer which produce both the positiveair ions and the negative air ions.
5. The method as claimed in claim 4, wherein said ionisercomprises at least a pair of air ionizing electrodes anda D.C. high voltage supply which produces both positiveand negative high voltages to apply voltages of oppositepolarities to said ionizing electrodes.
6. The method as claimed in claim 5, said ionizer furthercomprising means for interchanging the polarities of saidionizing electrodes at a predetermined interval.
7. The method as claimed in claim 3, wherein the air ions aresupplied by an air ionizer which comprises at least oneair ionizing electrode, a D.C. high voltage supply producing both positive and negative high voltages toapply a voltage of either of polarity to said ionizingelectrode and means for interchanging the polarity of saidionizing electrode at a predetermined interval.
8. The method as claimed in claim 1, wherein the particlesare sprayed on a surface of liquid to form the coating onthe surface.
9. The method as claimed in claim 8, wherein an object ispressed onto the surface of the liquid and the coating istransferred to a surface of the object by a liquidpressure.
10. A spray booth apparatus for spraying particles to anobject by continuously supplying air ions of positive andnegative air ions, said apparatus comprising:

    a chamber for accommodating the object; and

    an air ionizer which is provided at a ceiling or a sidewall of the chamber, and said ionizer receives an air froman outside of the chamber and produce the positive andnegative air ions to supply in said chamber.
11. The apparatus as claimed in claim 8, wherein said ionizercomprises at least a pair of air ionizing electrodes anda D.C. high voltage supply which produces both positiveand negative high volrages to apply voltages of oppositepolarities to said ionizing electrodes.
12. The apparatus as claimed in claim 9, said ionizer furthercomprising means for interchanging the polarities of saidionizing electrodes at a predetermined interval.
13. The apparatus as claimed in claim 8, wherein said ionizercomprises at least one air ionizing electrode, a D.C. highvoltage supply producing both positive and negative highvoltages to apply a voltage of either of polarity to saidionizing electrode and means for interchanging thepolarity of said ionizing electrode at a predeterminedinterval.
14. The apparatus as claimed in claim 8, wherein said ionizercomprises a plurality of wire electrodes which areaccommodated in elongate cartridges and each saidcartridges has a slit which extends in a longitudinaldirection of said cartridge and faces downwardly to injectthe air ions therethrough.
15. The apparatus as claimed in claim 14, wherein upperportions of said each cartridges are fixed to firstsupporting members having hollow portions, saidcartridges and said first supporting members arecommunicated and the air is introduced to said electrodesvia the hollow portions of the first supporting members.
16. The apparatus as claimed is claim 15, wherein one endsof the first supporting members are fixed to a secondsupporting member which extends perpendicularly to thefirst supporting members and has a hollow portion, thefirst supporting members and the second supporting memberare communicated and an air hose which introduces the airfrom the outside of the chamber is connected to one endof the second supporting member.
17. The apparatus as claimed in claim 16, wherein an airblower is provided adjacent to an air inlet to introducethe air to the electrodes.
18. The apparatus as claimed in claim 17, wherein a rotationof the air blower and a charging of the electrode aresynchronized.
19. The apparatus as claimed in claim 17, wherein an airfilter is provided at the air inlet to clean the air whichis to be supplied to the electrodes.

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